Some people are just a pain in the arse to train with and would rather feel important by telling you something you are doing wrong than get it right themselves. Deal with your problems one step at a time. A good teacher is one that tells you only what you are ready to hear.

As for martial/spiritual aspect. My view is that only by understanding aikido and attacks as potenitally lethal can you understand the spiritual aspect. Aikido is not about being 'nice' it is understanding life and death. I think, ironically, that the more you accept death the less egotistical you are about your training and the more you can let go. You are not looking to 'win' you are looking to perfect your aikido. Don't try and impress people (inc. sensei), just work out what is most effective for you and practise it. It is your aikido and you are the only one responsible for making it good.

Relaxation and thinking are difficult to do simultaneously. People may be asking too much from you. Focus on learning the techniques first, and then you can start doing aikido. Above all, don't worry!